1. Field of the Invention
The present invention relates to an engine start control device, and more particularly, to an engine start control device of a type using a starter motor.
2. Description of the Related Art
There has conventionally been known a start control device of a type which starts an engine by rotating a crankshaft by a starter motor. In this engine start control device, an idle speed control valve (ISCV) for controlling an idle speed is provided in a bypass channel bypassing a throttle valve of the engine. The ISCV is structured to be capable of adjusting its opening degree by a stepping motor, and at the engine start time, it is possible to ensure an intake amount suitable for starting the engine by adjusting the opening degree of the ISCV to a target opening degree.
In the engine start control device, the driving of the stepping motor of the ISCV is controlled by a control unit. The control unit is connected to a battery via an ignition switch and is structured to be supplied with power when the ignition switch is turned on. Generally, the battery which supplies the power to the control unit is also used for supplying power to a starter motor.
As described above, at the engine start time, it is necessary to realize the intake amount suitable for the start by adjusting the opening degree of the ISCV to the target opening degree. Therefore, when the ignition switch is turned on, the control unit drives the stepping motor so that the ISCV is moved to the target opening degree. Here, when the starter motor is driven in order to start the engine, a large current passes through the starter motor, so that the supply voltage of the battery temporarily decreases. This results in a decrease also in the supply voltage to the control unit to stop the control unit, and when the supply voltage of the battery thereafter recovers to return to a predetermined value, there sometimes occurs resetting that is the reactivation of the control unit.
Not capable of distinguishing the reactivation due to the resetting and the activation caused when the ignition switch is turned on, the control unit tries to move the ISCV to the target opening degree again at the time of the reactivation due to the resetting, as in the case where the ignition switch is turned on. The target opening degree of the ISCV is customarily set as a step amount from a reference position, with a position of the ISCV at an instant when the control unit is activated being defined as the reference. Therefore, when the control unit is reset after changing the position of the ISCV in response to the turning on of the ignition switch, the control unit tries to further change the ISCV by a predetermined step amount, with the changed position being defined as the reference position. As a result, the ISCV is brought into a state greatly deviating from the target opening degree, which causes problems such as poor start and an unstable behavior of the engine.
In order to solve such problems, Patent Document 1, for instance, discloses an idle speed control device which is capable of distinguishing the resetting due to an off operation of an ignition switch and the resetting due to low-voltage instantaneous interruption of a CPU, and does not perform a valve opening operation of an idle speed control valve when the resetting of the CPU is due to the low-voltage instantaneous interruption.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2010-223030
In the above-described Patent Document 1, since the ISCV is not operated when the resetting due to the voltage decrease occurs, it is not possible to cope with such a case where the opening degree of the ISCV is not properly maintained at the time of the resetting, for instance. Therefore, it is hard to say that the problems such as the poor start and the unstable behavior of the engine can be fully prevented.